What this page sets up
The calculator opens in date mode: pick the start and end dates and the days in a year, and it counts the days between them. The start date defaults to today and the end date to a year from now. The simple interest card gives the interest the way most loans, late-payment charges and court judgments work it out, on the balance only. The compound card shows the same days with interest compounded daily, the way savings accounts pay it. Under the stats, Simple interest per day is what one day costs or earns on the starting balance.
Counting the days
The day count includes the start date and not the end date, so a loan taken out on March 1 and repaid on March 31 accrues 30 days of interest. Leap days count like any other day. Choose 365 (actual/365) unless your contract says interest is computed on a 360-day year; the difference is about 1.4% more interest with 360.
Using it for late payments and judgments
For a debt that accrues interest at a fixed yearly rate, enter the amount owed, the rate and the dates, and read the simple interest. Courts and statutes set their own rates and rules, and some change them every year or quarter, so look up the rate that applies where you are and for the period in question. If partial payments were made along the way, work out each period between payments separately.
Interest per day on $10,000
Simple interest per day and over 30 days at common rates, by both day counts:
| Rate a year | Per day, actual/365 | 30 days, actual/365 | Per day, actual/360 | 30 days, actual/360 |
|---|---|---|---|---|
| 3% | $0.82 | $24.66 | $0.83 | $25.00 |
| 5% | $1.37 | $41.10 | $1.39 | $41.67 |
| 8% | $2.19 | $65.75 | $2.22 | $66.67 |
| 10% | $2.74 | $82.19 | $2.78 | $83.33 |
| 12% | $3.29 | $98.63 | $3.33 | $100.00 |
| 18% | $4.93 | $147.95 | $5.00 | $150.00 |
For any other balance, scale the figures: 25,000 earns 2.5 times the amounts shown. Not financial or legal advice.